The ATO administers income tax and capital gains tax in Australia. It draws a line between an investor, whose disposals are capital and who may access the australia-cgt-discount after twelve months, and a share trader carrying on a business, whose gains are ordinary income and whose holdings are trading stock.
Data matching is extensive. The ATO receives information from Australian brokers, share registries, and cryptocurrency exchanges, and prefills much of it, so undeclared disposals are found routinely.
This is general information, not tax advice. Australian rules and ATO rulings change, and whether you are an investor or a trader depends on your own pattern of activity, so get advice from a registered tax agent.
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